migrate/cpu-throttle: Add max-cpu-throttle migration parameter

Currently, the default maximum CPU throttle for migration is
99(CPU_THROTTLE_PCT_MAX). This is too big and can make a remarkable
performance effect for the guest. We see a lot of packets latency
exceed 500ms when the CPU_THROTTLE_PCT_MAX reached. This patch set
adds a new max-cpu-throttle parameter to limit the CPU throttle.

Signed-off-by: Li Qiang <liq3ea@gmail.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

3 files changed, 26 insertions, 2 deletions

diff --git a/migration/migration.c b/migration/migration.c
index b7d9854bda..570da6c0e7 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -71,6 +71,7 @@
 /* Define default autoconverge cpu throttle migration parameters */
 #define DEFAULT_MIGRATE_CPU_THROTTLE_INITIAL 20
 #define DEFAULT_MIGRATE_CPU_THROTTLE_INCREMENT 10
+#define DEFAULT_MIGRATE_MAX_CPU_THROTTLE 99
 
 /* Migration XBZRLE default cache size */
 #define DEFAULT_MIGRATE_XBZRLE_CACHE_SIZE (64 * 1024 * 1024)
@@ -697,6 +698,8 @@ MigrationParameters *qmp_query_migrate_parameters(Error **errp)
     params->xbzrle_cache_size = s->parameters.xbzrle_cache_size;
     params->has_max_postcopy_bandwidth = true;
     params->max_postcopy_bandwidth = s->parameters.max_postcopy_bandwidth;
+    params->has_max_cpu_throttle = true;
+    params->max_cpu_throttle = s->parameters.max_cpu_throttle;
 
     return params;
 }
@@ -1043,6 +1046,15 @@ static bool migrate_params_check(MigrationParameters *params, Error **errp)
         return false;
     }
 
+    if (params->has_max_cpu_throttle &&
+        (params->max_cpu_throttle < params->cpu_throttle_initial ||
+         params->max_cpu_throttle > 99)) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
+                   "max_cpu_throttle",
+                   "an integer in the range of cpu_throttle_initial to 99");
+        return false;
+    }
+
     return true;
 }
 
@@ -1110,6 +1122,9 @@ static void migrate_params_test_apply(MigrateSetParameters *params,
     if (params->has_max_postcopy_bandwidth) {
         dest->max_postcopy_bandwidth = params->max_postcopy_bandwidth;
     }
+    if (params->has_max_cpu_throttle) {
+        dest->max_cpu_throttle = params->max_cpu_throttle;
+    }
 }
 
 static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
@@ -1185,6 +1200,9 @@ static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
     if (params->has_max_postcopy_bandwidth) {
         s->parameters.max_postcopy_bandwidth = params->max_postcopy_bandwidth;
     }
+    if (params->has_max_cpu_throttle) {
+        s->parameters.max_cpu_throttle = params->max_cpu_throttle;
+    }
 }
 
 void qmp_migrate_set_parameters(MigrateSetParameters *params, Error **errp)
@@ -1962,7 +1980,6 @@ static int64_t migrate_max_postcopy_bandwidth(void)
     return s->parameters.max_postcopy_bandwidth;
 }
 
-
 bool migrate_use_block(void)
 {
     MigrationState *s;
@@ -3160,6 +3177,9 @@ static Property migration_properties[] = {
     DEFINE_PROP_SIZE("max-postcopy-bandwidth", MigrationState,
                       parameters.max_postcopy_bandwidth,
                       DEFAULT_MIGRATE_MAX_POSTCOPY_BANDWIDTH),
+    DEFINE_PROP_UINT8("max-cpu-throttle", MigrationState,
+                      parameters.max_cpu_throttle,
+                      DEFAULT_MIGRATE_MAX_CPU_THROTTLE),
 
     /* Migration capabilities */
     DEFINE_PROP_MIG_CAP("x-xbzrle", MIGRATION_CAPABILITY_XBZRLE),
@@ -3230,6 +3250,7 @@ static void migration_instance_init(Object *obj)
     params->has_x_multifd_page_count = true;
     params->has_xbzrle_cache_size = true;
     params->has_max_postcopy_bandwidth = true;
+    params->has_max_cpu_throttle = true;
 
     qemu_sem_init(&ms->postcopy_pause_sem, 0);
     qemu_sem_init(&ms->postcopy_pause_rp_sem, 0);
diff --git a/migration/migration.h b/migration/migration.h
index 64a7b33735..eb0c04a7b4 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -266,6 +266,7 @@ bool migrate_colo_enabled(void);
 
 bool migrate_use_block(void);
 bool migrate_use_block_incremental(void);
+int migrate_max_cpu_throttle(void);
 bool migrate_use_return_path(void);
 
 bool migrate_use_compression(void);
diff --git a/migration/ram.c b/migration/ram.c
index fa79d0a5b9..1e5c45a514 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1391,13 +1391,15 @@ static void mig_throttle_guest_down(void)
     MigrationState *s = migrate_get_current();
     uint64_t pct_initial = s->parameters.cpu_throttle_initial;
     uint64_t pct_icrement = s->parameters.cpu_throttle_increment;
+    int pct_max = s->parameters.max_cpu_throttle;
 
     /* We have not started throttling yet. Let's start it. */
     if (!cpu_throttle_active()) {
         cpu_throttle_set(pct_initial);
     } else {
         /* Throttling already on, just increase the rate */
-        cpu_throttle_set(cpu_throttle_get_percentage() + pct_icrement);
+        cpu_throttle_set(MIN(cpu_throttle_get_percentage() + pct_icrement,
+                         pct_max));
     }
 }